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* Copyright (c) 2012, 2013, Oracle and/or its affiliates. All rights reserved.
* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
*
* This code is free software; you can redistribute it and/or modify it
* under the terms of the GNU General Public License version 2 only, as
* published by the Free Software Foundation. Oracle designates this
* particular file as subject to the "Classpath" exception as provided
* by Oracle in the LICENSE file that accompanied this code.
*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
* You should have received a copy of the GNU General Public License version
* 2 along with this work; if not, write to the Free Software Foundation,
* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
*
* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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package com.landawn.abacus.util;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Set;
import com.landawn.abacus.util.function.Consumer;
import com.landawn.abacus.util.function.Function;
import com.landawn.abacus.util.function.Predicate;
import com.landawn.abacus.util.function.Supplier;
import com.landawn.abacus.util.function.ToBooleanFunction;
import com.landawn.abacus.util.function.ToByteFunction;
import com.landawn.abacus.util.function.ToCharFunction;
import com.landawn.abacus.util.function.ToDoubleFunction;
import com.landawn.abacus.util.function.ToFloatFunction;
import com.landawn.abacus.util.function.ToIntFunction;
import com.landawn.abacus.util.function.ToLongFunction;
import com.landawn.abacus.util.function.ToShortFunction;
import com.landawn.abacus.util.stream.Stream;
/**
* Note: It's copied from OpenJDK at: http://hg.openjdk.java.net/jdk8u/hs-dev/jdk
*
*
* A container object which may or may not contain a non-null value.
* If a value is present, {@code isPresent()} will return {@code true} and
* {@code get()} will return the value.
*
* Additional methods that depend on the presence or absence of a contained
* value are provided, such as {@link #or(java.lang.Object) orElse()}
* (return a default value if value not present) and
* {@link #ifPresent(java.util.function.Consumers) ifPresent()} (execute a block
* of code if the value is present).
*
*
This is a value-based
* class; use of identity-sensitive operations (including reference equality
* ({@code ==}), identity hash code, or synchronization) on instances of
* {@code Optional} may have unpredictable results and should be avoided.
*
* @since 1.8
*/
public final class Optional {
/**
* Common instance for {@code empty()}.
*/
private static final Optional EMPTY = new Optional<>();
/**
* If non-null, the value; if null, indicates no value is present
*/
private final T value;
/**
* Constructs an empty instance.
*
* @implNote Generally only one empty instance, {@link Optional#EMPTY},
* should exist per VM.
*/
private Optional() {
this.value = null;
}
/**
* Returns an empty {@code Optional} instance. No value is present for this
* Optional.
*
* @apiNote Though it may be tempting to do so, avoid testing if an object
* is empty by comparing with {@code ==} against instances returned by
* {@code Optional.empty()}. There is no guarantee that it is a singleton.
* Instead, use {@link #isPresent()}.
*
* @param Type of the non-existent value
* @return an empty {@code Optional}
*/
public static Optional empty() {
@SuppressWarnings("unchecked")
Optional t = (Optional) EMPTY;
return t;
}
/**
* Constructs an instance with the value present.
*
* @param value the non-null value to be present
* @throws NullPointerException if value is null
*/
private Optional(T value) {
this.value = N.requireNonNull(value);
}
/**
* Returns an {@code Optional} with the specified present non-null value.
*
* @param the class of the value
* @param value the value to be present, which must be non-null
* @return an {@code Optional} with the value present
* @throws NullPointerException if value is null
*/
public static Optional of(T value) {
return new Optional<>(value);
}
/**
* Returns an {@code Optional} describing the specified value, if non-null,
* otherwise returns an empty {@code Optional}.
*
* @param the class of the value
* @param value the possibly-null value to describe
* @return an {@code Optional} with a present value if the specified value
* is non-null, otherwise an empty {@code Optional}
*/
public static Optional ofNullable(T value) {
return value == null ? (Optional) empty() : of(value);
}
/**
* If a value is present in this {@code Optional}, returns the value,
* otherwise throws {@code NoSuchElementException}.
*
* @return the non-null value held by this {@code Optional}
* @throws NoSuchElementException if there is no value present
*
* @see Optional#isPresent()
*/
public T get() {
if (isPresent()) {
return value;
} else {
throw new NoSuchElementException("No value present");
}
}
/**
* Return {@code true} if there is a value present, otherwise {@code false}.
*
* @return {@code true} if there is a value present, otherwise {@code false}
*/
public boolean isPresent() {
return value != null;
}
/**
* If a value is present, invoke the specified consumer with the value,
* otherwise do nothing.
*
* @param action block to be executed if a value is present
* @throws NullPointerException if value is present and {@code consumer} is
* null
*/
public void ifPresent(Consumer action) {
if (isPresent()) {
action.accept(value);
}
}
/**
* If a value is present, performs the given action with the value, otherwise performs the given empty-based action.
*
* @param action
* @param emptyAction
*/
public void ifPresentOrElse(Consumer action, Runnable emptyAction) {
if (isPresent()) {
action.accept(value);
} else {
emptyAction.run();
}
}
/**
* If a value is present, and the value matches the given predicate,
* return an {@code Optional} describing the value, otherwise return an
* empty {@code Optional}.
*
* @param predicate a predicate to apply to the value, if present
* @return an {@code Optional} describing the value of this {@code Optional}
* if a value is present and the value matches the given predicate,
* otherwise an empty {@code Optional}
* @throws NullPointerException if the predicate is null
*/
public Optional filter(Predicate predicate) {
N.requireNonNull(predicate);
if (isPresent() && predicate.test(value)) {
return this;
} else {
return empty();
}
}
/**
* If a value is present, apply the provided mapping function to it,
* and if the result is non-null, return an {@code Optional} describing the
* result. Otherwise return an empty {@code Optional}.
*
* @apiNote This method supports post-processing on optional values, without
* the need to explicitly check for a return status. For example, the
* following code traverses a stream of file names, selects one that has
* not yet been processed, and then opens that file, returning an
* {@code Optional}:
*
* {@code
* Optional fis =
* names.stream().filter(name -> !isProcessedYet(name))
* .findFirst()
* .map(name -> new FileInputStream(name));
* }
*
* Here, {@code findFirst} returns an {@code Optional}, and then
* {@code map} returns an {@code Optional} for the desired
* file if one exists.
*
* @param The type of the result of the mapping function
* @param mapper a mapping function to apply to the value, if present
* @return an {@code Optional} describing the result of applying a mapping
* function to the value of this {@code Optional}, if a value is present,
* otherwise an empty {@code Optional}
* @throws NullPointerException if the mapping function is null
*/
public Optional map(final Function mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return (Optional) Optional.ofNullable(mapper.apply(value));
} else {
return empty();
}
}
public OptionalBoolean mapToBoolean(final ToBooleanFunction mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return OptionalBoolean.of(mapper.applyAsBoolean(value));
} else {
return OptionalBoolean.empty();
}
}
public OptionalChar mapToChar(final ToCharFunction mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return OptionalChar.of(mapper.applyAsChar(value));
} else {
return OptionalChar.empty();
}
}
public OptionalByte mapToByte(final ToByteFunction mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return OptionalByte.of(mapper.applyAsByte(value));
} else {
return OptionalByte.empty();
}
}
public OptionalShort mapToShort(final ToShortFunction mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return OptionalShort.of(mapper.applyAsShort(value));
} else {
return OptionalShort.empty();
}
}
public OptionalInt mapToInt(final ToIntFunction mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return OptionalInt.of(mapper.applyAsInt(value));
} else {
return OptionalInt.empty();
}
}
public OptionalLong mapToLong(final ToLongFunction mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return OptionalLong.of(mapper.applyAsLong(value));
} else {
return OptionalLong.empty();
}
}
public OptionalFloat mapToFloat(final ToFloatFunction mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return OptionalFloat.of(mapper.applyAsFloat(value));
} else {
return OptionalFloat.empty();
}
}
public OptionalDouble mapToDouble(final ToDoubleFunction mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return OptionalDouble.of(mapper.applyAsDouble(value));
} else {
return OptionalDouble.empty();
}
}
/**
* If a value is present, apply the provided {@code Optional}-bearing
* mapping function to it, return that result, otherwise return an empty
* {@code Optional}. This method is similar to {@link #map(Function)},
* but the provided mapper is one whose result is already an {@code Optional},
* and if invoked, {@code flatMap} does not wrap it with an additional
* {@code Optional}.
*
* @param The type parameter to the {@code Optional} returned by
* @param mapper a mapping function to apply to the value, if present
* the mapping function
* @return the result of applying an {@code Optional}-bearing mapping
* function to the value of this {@code Optional}, if a value is present,
* otherwise an empty {@code Optional}
* @throws NullPointerException if the mapping function is null or returns
* a null result
*/
public Optional flatMap(Function> mapper) {
N.requireNonNull(mapper);
if (isPresent()) {
return N.requireNonNull(mapper.apply(value));
} else {
return empty();
}
}
/**
* Return the value if present, otherwise return {@code other}.
*
* @param other the value to be returned if there is no value present, may
* be null
* @return the value, if present, otherwise {@code other}
*/
public T orElse(T other) {
return isPresent() ? value : other;
}
/**
* Return the value if present, otherwise invoke {@code other} and return
* the result of that invocation.
*
* @param other a {@code Supplier} whose result is returned if no value
* is present
* @return the value if present otherwise the result of {@code other.get()}
* @throws NullPointerException if value is not present and {@code other} is
* null
*/
public T orElseGet(Supplier other) {
return isPresent() ? value : other.get();
}
/**
* Return the contained value, if present, otherwise throw an exception
* to be created by the provided supplier.
*
* @apiNote A method reference to the exception constructor with an empty
* argument list can be used as the supplier. For example,
* {@code IllegalStateException::new}
*
* @param Type of the exception to be thrown
* @param exceptionSupplier The supplier which will return the exception to
* be thrown
* @return the present value
* @throws X if there is no value present
* @throws NullPointerException if no value is present and
* {@code exceptionSupplier} is null
*/
public T orElseThrow(Supplier exceptionSupplier) throws X {
if (isPresent()) {
return value;
} else {
throw exceptionSupplier.get();
}
}
public Stream stream() {
return isPresent() ? Stream.of(value) : Stream. empty();
}
public java.util.Optional __() {
return isPresent() ? java.util.Optional.of(value) : java.util.Optional. empty();
}
/**
* Returns a {@code List} with the value if it presents, otherwise an empty {@code List}.
*
* @return
*/
public List toList() {
return isPresent() ? N.asList(value) : new ArrayList();
}
/**
* Returns a {@code Set} with the value if it presents, otherwise an empty {@code Set}.
*
* @return
*/
public Set toSet() {
return isPresent() ? N.asSet(value) : new HashSet();
}
/**
* Indicates whether some other object is "equal to" this Optional. The
* other object is considered equal if:
*
* - it is also an {@code Optional} and;
*
- both instances have no value present or;
*
- the present values are "equal to" each other via {@code equals()}.
*
*
* @param obj an object to be tested for equality
* @return {code true} if the other object is "equal to" this object
* otherwise {@code false}
*/
@Override
public boolean equals(Object obj) {
if (this == obj) {
return true;
}
if (obj instanceof Optional) {
Optional other = (Optional) obj;
return N.equals(value, other.value);
}
return false;
}
/**
* Returns the hash code value of the present value, if any, or 0 (zero) if
* no value is present.
*
* @return hash code value of the present value or 0 if no value is present
*/
@Override
public int hashCode() {
return N.hashCode(value);
}
/**
* Returns a non-empty string representation of this Optional suitable for
* debugging. The exact presentation format is unspecified and may vary
* between implementations and versions.
*
* @implSpec If a value is present the result must include its string
* representation in the result. Empty and present Optionals must be
* unambiguously differentiable.
*
* @return the string representation of this instance
*/
@Override
public String toString() {
return value != null ? String.format("Optional[%s]", value) : "Optional.empty";
}
}